As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased as an energy source for the mobile devices.
Depending upon kinds of external devices in which the secondary batteries are used, the secondary batteries may be used in the form of a single battery or in the form of a battery pack having a plurality of unit cells electrically connected with each other. For example, small-sized devices, such as mobile phones, can be operated for a predetermined period of time with the output and the capacity of one battery. On the other hand, a battery pack needs to be used in medium- or large-sized devices, such as laptop computers, portable digital versatile disc (DVD) players, small-sized personal computers (PCs), electric vehicles, and hybrid electric vehicles, because high output and large capacity are necessary for the medium- or large-sized devices.
The battery pack is manufactured by connecting a protection circuit to a battery core pack having a plurality of unit cells connected in series and/or in parallel with each other. When prismatic batteries or pouch-shaped batteries are used as the unit cells, the prismatic batteries or the pouch-shaped batteries are stacked one on another such that large-sized surfaces of the prismatic batteries or the pouch-shaped batteries face each other, and then electrode terminals of the prismatic batteries or the pouch-shaped batteries are connected with each other by connecting members, such as bus bars. Consequently, when a three-dimensional battery pack having a hexahedral structure is to be manufactured, the prismatic batteries or the pouch-shaped batteries are favorable as the unit cells.
On the other hand, cylindrical batteries generally have electric capacities larger than the prismatic batteries or the pouch-shaped batteries. However, it is difficult to arrange the cylindrical batteries in a stacked structure due to the outer appearance of the cylindrical batteries. When the battery pack is constructed generally in a line-type structure or in a plane-type structure, though, the cylindrical batteries are structurally more advantageous than the prismatic batteries or the pouch-shaped batteries.
Consequently, a battery pack having a plurality of cylindrical batteries connected in parallel and in series with each other is widely used in laptop computers, portable DVD players, and portable PCs. For example, the battery pack is usually constructed in a 2P (parallel)-3S (series) line-type structure, a 2P-3S plane-type structure, a 2P-4S line-type structure, or a 2P-4S plane-type structure.
The parallel connection structure is accomplished by arranging two or more cylindrical batteries in the lateral direction while electrode terminals of the cylindrical batteries are oriented in the same direction, and connecting the electrode terminals of the cylindrical batteries with each other using connecting members by welding. Hereinafter, the cylindrical batteries connected in parallel will be referred to as “banks.”
The series connection structure is accomplished by arranging two or more cylindrical batteries in the longitudinal direction such that electrode terminals of the cylindrical batteries having opposite polarities are successively disposed one after another, or arranging two or more cylindrical batteries in the lateral direction while electrode terminals of the cylindrical batteries are oriented in opposite directions, and connecting the electrode terminals of the cylindrical batteries with each other using connecting members by welding.
The electrical connection between the cylindrical batteries is generally accomplished by spot welding using thin plate-shaped connecting members, such as nickel plates. A protection circuit is connected to the battery core pack constructed in the parallel and/or series connection structure so as to manufacture a battery pack.
Whenever the design of the battery pack is changed, however, the connecting members must be modified such that the connecting members are suitable for the changed design of the battery pack. As a result, the manufacturing costs of the battery pack are increased. This problem may occur even when the electrical connection between general batteries, such as prismatic batteries, is performed.